As oil well drilling becomes increasingly complex, the importance of collecting and analyzing downhole data while drilling increases. When performing subterranean operations such as drilling or completing wells, it is often desirable to monitor, locate, and image deformations in the well casing and/or the tubing used. It is also desirable to monitor the integrity of the cement layer around the well to detect any problems in the cement or changes in the formation during hydrocarbon production near the well or well flooding. Well logging instruments are often used to probe subsurface formations to determine formation characteristics.
Sonic tools are an example of well logging tools that may be used to provide information regarding subsurface acoustic properties that can be used to analyze the formation. This information may include, for example, compressional wave speed, shear wave speed, wellbore modes, and formation slowness. The information obtained by acoustic measurements has a number of applications, including, but not limited to, seismic correlation, petrophysics, rock mechanics and other applications.
During a typical sonic logging of a formation, an acoustic logging instrument or tool is lowered into a wellbore that transverses a formation of interest. The acoustic logging tool may be mounted to the drill collar or other devices and directed downhole. Conventional acoustic logging tools may include acoustic transducer elements such as a piezoelectric element. Generally, the acoustic transducer can convert electric energy to acoustic energy as well as acoustic energy to electric energy and may act as an acoustic source or an acoustic sensor. The acoustic logging tool may include a transmitter which performs as an acoustic source and emits acoustic energy into the formation and one or more receivers or acoustic sensors that receive acoustic energy. Once the acoustic logging tool is lowered into the formation, the transmitter may be periodically actuated to emit pulses of acoustic energy as acoustic waves into the wellbore. The emitted acoustic waves propagate through the wellbore wall producing a reflection that is then detected by the receiver(s) which produce an electric signal in response. Attributes of the reflected acoustic waves that are detected at the receiver(s) may then be used to characterize subsurface properties of the formation of interest.
However, the receiver(s) of the acoustic logging tool are typically also sensitive to undesired acoustic noise that may result from normal drilling operations. For instance, the undesired acoustic noise may propagate with reduced attenuation through a hard steel drill collar. The acoustic noise may then couple to the receiver of the acoustic logging tool and be converted into electrical noise along with the desired signal. This background noise may be a result of the downhole operations or produced by other acoustic sources and therefore may introduce an error in the measurements by the acoustic logging tool. It is therefore desirable to provide a logging tool that can minimize or eliminate the susceptibility of the logging tool to the background noise.
Additionally, traditional logging tools often involve complex downhole equipment and sensors which may be expensive to operate and maintain. Therefore, there is a need for a simpler, lower-cost method for monitoring wellbore conditions.
The disclosure may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the disclosure being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.